A breath of fresh air is something we all take for granted, even when that air's been bottled
up inside a tank. But for diver Mike Daniels, who was diving with Aldora Divers in Cozumel last November, the air
that came his way was anything but. He was in a swimthrough with 1800 psi in his steel tank when he suddenly found
himself unable to draw any air at all from either his primary or alternate supply. Fortunately, Aldora's divemaster,
Alexandra, was quick to respond, and they ascended normally with a five-minute safety stop. When they got back
on the boat, they discovered that both the tank valve and first stage were completely clogged with rust that Daniels
felt could only have come from Aldora's steel tank. Daniels was understandably upset, and Dave Dillehay of Aldora
Divers bore the brunt of his wrath. Like many divers, Dillehay likes steel tanks, saying that the extra air capacity
"provides a real extra margin of safety" on long dives. (He also points out that aluminum tanks aren't
corrosion-free either, although oxidation doesn't tend to accumulate as rapidly as with steel tanks.) Dillehay
had believed Aldora's routine six-month tank inspections were frequent enough to detect any problems before they
became serious. In fact, Dillehay says that Daniels' tank had been inspected in September and was clean at the
time of inspection. He believes that the rapid contamination was the result of seawater incursion that probably
occurred when a tank was emptied during an unsupervised beach dive, and Aldora has since banned the use of steel
tanks on beach dives. They've also stepped up maintenance efforts: they completed a visual inspection of all tanks
within a few days of the incident, and, from now on, each tank will undergo an inverted, agitated flow test each
month and be visually inspected every six months.

It's hard to believe that a tank can rust as quickly as Aldora's apparently did, but studies have shown that seawater,
tank pressure, and tropical temperatures all significantly accelerate oxidation. In 1976, for example, the University
of Rhode Island tested new pressurized cylinders to which they'd added 500 ml of salt water. The tanks were stored
in a horizontal position at a temperature of 105° F. for 100 days. By the end of the test period, tanks were
already severely corroded, and some had lost over two-thirds of their wall thickness. Because tanks that contained
fresh water or were unpressurized or stored vertically had significantly less corrosion, the study recommended
handling procedures such as fresh water rinsing and drying, storing tanks with minimum pressure, and storing them
in a vertical position.

Since high-pressure steel tanks are gaining popularity, what else can dive operators do to make sure that their
tanks remain rust free? Undercurrent spoke with Paul Caputo of Quiescence Diving Services in Key Largo, who handles
high-pressure steel tanks in large volume. According to Caputo, frequent inspection is important, but, because
even a little water can be the start of a serious rust problem and corrosion can occur very quickly in tropical
temperatures, Caputo emphasizes the importance of keeping water out of tanks in the first place. Since air pressure
inside the tank tends to keep water out, tanks are most likely to take on water either when the tanks are filled
or if they've been emptied completely during the course of a dive, allowing water to be drawn in.

Tanks are vulnerable to taking on water during filling because some tank valves tend to catch water from boat spray
or other sources. If the valve isn't cracked open briefly and blown out before installing the fill whip, the water
sitting in the valve will be pushed into the tank when it's filled. If a large percentage of tanks at an operation
had rust problems, Caputo said he would suspect that water was being introduced during filling. Since Aldora found
contamination in only a few of its tanks, however, it's more likely that contamination occurred when these tanks
were emptied during dives (which was also Dillehay's assessment of the problem). Quiescence's own tank maintenance
program calls for visual inspection of all tanks three or four times a year and immediate inspection of any tank
that comes back empty. Additionally, tank valves are always opened briefly to blow out any water sitting in the
valve before the tanks are filled. Obviously, the thousand-dollar question is, "Are the tank maintenance efforts
in place at Aldora and other operations adequate to prevent other divers from experiencing the problems that Daniels
did?" Dave Dillehay obviously thinks so. In fact, Dillehay's so confident that they have a handle on the problem
that he gave Undercurrent a thousand-dollar answer: "Pay $10 to open any Aldora tank, and I will pay $1000
for every flake of rust found. For those truly convinced of our lingering 'serious tank problem,' that could be
an easy way to pay for their next dive vacation."